The invention comprises a process for simultaneous manufacture of acetylene and calcium chloride from calcium carbide and hydrogen chloride.
In the currently practiced art, calcium carbide is charged to a large tank containing water and which is outfitted with slow moving stirring paddles. The carbide is dropped onto the surface of the water where it is allowed to react spontaneously. Acetylene gas is withdrawn from the top of the tank while calcium hydroxide and other impurities settle to the bottom of the tank. The reactor is cooled by internal coils containing cooling water or by spraying cold water on the exterior of the tank or both. The calcium hydroxide produced, along with its impurities, is discharged, stockpiled and disposed of as a low value neutralizer for industrial acid streams or for maintaining pH balance in sewage plants. Depending upon the application, acetylene is compressed and stored in high pressure vessels or, in cases where it is used as a chemical feedstock, is pipelined to a nearby chemicals processing plant.
The current problems with the state-of-the-art technology are:
A. Uncontrolled contact of the carbide with the water, resulting in lower reaction rate control and the possibility of incandescence. Incandescence results when calcium carbide particles are buoyed by the evolution of acetylene and rise to the surface of the water where they react violently but without the benefit of cooling that prevails when the particles are submerged. The lack of cooling and the high exothermicity of the reaction may result in a localized temperature rise which heats the particle to incandescent or glowing temperatures. If the pressure of the acetylene is higher than approximately 27 pounds per square inch absolute, this condition may initiate detonation or deflagration reactions within the acetylene, resulting in a substantial pressure rise, rupture of the vessel, and uncontrolled release of the contents This condition presents a significant fire and safety hazard. Thus, poor reaction control results in a higher probability for adverse chemical reactions and necessitates the requirement that the primary reaction vessel be operated at a low operating pressure.
B. Currently practiced technology utilizes a single reactor vessel of a stirred tank reactor design. Because of the inherent characteristics of a stirred tank reactor large vessels are required in relationship to the throughout of carbide to avoid discharge of unreacted carbide. In practice, slow mixing results in a reactor which is neither an ideal CSTR or ideal plug flow reactor and for which little is known of the local processes occurring. This condition results in poor rate control and unsteady operation.
C. Currently practiced technology results in extremely low utilization of the available heat evolved in the exothermic reaction between calcium carbide and water. In currently practiced technology, little or none of the heat produced is used. This heat amounts to about 20% of the available chemical energy in the reactor and is wasted through the requirements of cooling.
D. In currently practiced technology, little or no effort is made to improve the quality of the calcium hydroxide byproduct. Calcium hydroxide produced in acetylene manufacturing contains substantial impurities originating from coal, coke or limestone used in the manufacture of the calcium carbide. These impurities render the calcium hydroxide produced of extremely low or no market value.
It is an objective of the present invention to overcome those problems in its prior art identified above.
The process of the invention consists of a two-stage reactor system in which calcium carbide and water are reacted to form acetylene and calcium hydroxide. The calcium hydroxide is subsequently reacted with hydrogen chloride in a neutralizer to form calcium chloride. The calcium chloride may be marketed in an aqueous form or alternatively sent to a drying apparatus to produce marketable anhydrous calcium chloride.
The invention embodies a unique, dual reactor configuration in which water and calcium carbide are mixed in an entrained flow-type reactor The reaction is allowed to occur in a dilute aqueous phase with residence times such that the reaction proceeds to 60-90% completion while in the primary reactor. Entrained reaction products and unreacted feed material are carried overhead to the secondary reactor which consists of a dense phase, laminar plug-flow type reactor. Calcium hydroxide intermediate product is allowed to settle and is removed from the bottom of the reactor. Unreacted water is separated from the calcium hydroxide by use of an overflow wier and recycled to the primary reactor. The combination of the primary reactor and the secondary reactor are such that the majority of reaction occurs in a stirred-tank reactor type configuration which undergoes a transition in the secondary reactor to a plug-flow reactor configuration. The plug-flow reactor allows for the completion of the reaction of calcium carbide with water. In the presence of excess water, the reaction of calcium carbide with water is effectively a first order, irreversible reaction.